One existing technology used for generating colored metallic surfaces without using additional pigments is femtosecond or picosecond laser pulse writing, which produces laser-induced surface structures (LIPSSs) capable of engendering structural coloration on the metallic surfaces when illuminated by an incident light. These laser-induced, orderly surface patterns are spontaneously formed during laser irradiation (see, for example, FIG. 1). The orientation of the LIPSSs depends on the direction of the laser polarization, which is used to control the imprinted colors. For example, silver-white aluminum surfaces have been rendered to have gold, black, and grey colors by the laser-induced method.
LIPSSs, though highly reproducible, suffer from several drawbacks. First, it is challenging to predict and control the dimensions of the LIPSSs. Second, micro-gratings generated by LIPSSs are semi-regular, which adversely affects the efficiency of light diffraction and thus the colorization of the sample surface. Third, owing to material-specific laser-fluence, the effectiveness of coloration methods based on LIPSSs has not been verified for a wide variety of metallic surfaces. Fourth, the high cost of a femtosecond laser system and the long processing time (e.g., around 20 minutes for processing a 10 mm×10 mm copper sample) make the technology difficult to be adopted by industry for large-scale production.